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Original question:

UCC256304: Compatibility of this IC or topology for 24V/1000V 150W converter

UCC256304: Resonant capacitor topologies

Tim Finks60
Intellectual 300 points
Part Number: UCC256304
Other Parts Discussed in Thread: UCC25630-1EVM-291,

I note than some TI literature shows a single resonant capacitor in the transformer primary circuit to ground, while the EVM (UCC25630-1EVM-291, SLUUBQ8B) schematic and WebBench Power Designer include an apparent split arrangement of this capacitance to both rails. The design spread sheet shows a single capacitance.

Can someone compare and contrast the two alternatives? Is there a discussion of these choices available somewhere? In the split arrangement case, is the value of each capacitor is half of the total value needed for resonance?

  • 0
    TI__Mastermind 27145 points
    Hi Tim,

    Thanks for your interest in UCC256304. Split resonant capacitor will have the possibility to "pre-charge" the capacitor mid point to 1/2*Vin before the LLC converter is enabled. The benefit of this is during startup, the transformer will be driven symmetrically and have less risk for hard switching during startup. A single resonant capacitor to ground will start with 0V dc bias. The single resonant capacitor will need to be charged up before the transformer can be driven symmetrically, so there is more risk for hard switching during startup. The benefit of a single resonant capacitor is the layout is a little easier as you do not need to rout the resonant capacitor back to the input voltage

    With a split resonant capacitor, the value of each capacitor is half the total value of the resonant capacitor.

    Best Regards,
    Ben Lough